Having something to do with is not the same as being part of.To use your analogy ( again ), the library or course material at an astronomy department could easily make mention of astronomy comics as a facet of Astronomy History and it's impact on culture. Or I could ask you the same question I asked Morrison. Do you really thing the fictional film Close Encounter of the Third Kind has nothing to do with ufology?
A picture of a car has something to do with the car, but it's not part of that car. The steering wheel of that car is part of that car, a picture of that steering wheel isn't. The driver of that car has something to do with the car, but is not part of that car. The definition of that car is that actual car and the parts that it has, not those pictures or other stuff that just happens to have something to do with it.
It's just the same with fields like astronomy. Some things are actually part of it, others just have something to do with it. It makes no sense to claim some cartoon is astronomy if it has some picture of a star in it.